The present invention refers to a dispensing cartridge comprising a storage cylinder and a feeding piston in whose cylinder wall a sealing ring is inserted. Such a dispensing cartridge is known from EP-A-344,491 of the same applicant. At the time, this dispensing cartridge represented a progress over the state of the art, but tests have shown that it is capable of being improved. In Swiss Patent Application no. 02 079/90-1, disclosing a feeding piston having venting bores, a characteristic feature was essentially improved in order to prevent that material flowing out when the feeding piston is thrust forward and the venting bore is closed which will lead to disturbing soiling, and measures were further taken in order to ensure a quicker and simpler closure.
By contrast, the present invention is directed to improving another property of the dispensing cartridge, i.e. the preservation of the enclosed composition, more particularly the long-term storage of aggressive substances. While a sealing of the feeding piston in the cartridge wall by means of a sealing ring, generally an O-ring, is sufficient for many applications, aggressive substances which can attack this O-ring or substances having a low viscosity, i.e. extreme flowing properties, may result in situations where the use of a single sealing element poses a problem. Moreover, there are substances which are sensitive to the ingress of water vapor or of gases and thereby change their chemical properties.